feat: Add type conversion and parsing exercises

This commit is contained in:
Abdou Seck 2019-12-16 08:34:30 -05:00
parent fe10e06c37
commit 0c85dc1193
7 changed files with 302 additions and 0 deletions

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### Type conversions
Rust offers a multitude of ways to convert a value of a given type into another type.
The simplest form of type conversion is a type cast expression. It is denoted with the binary operator `as`. For instance, `println!("{}", 1 + 1.0);` would not compile, since `1` is an integer while `1.0` is a float. However, `println!("{}", 1 as f32 + 1.0)` should compile. The exercise [`using_as`](using_as.rs) tries to cover this.
Rust also offers traits that facilitate type conversions upon implementation. These traits can be found under the [`convert`](https://doc.rust-lang.org/std/convert/index.html) module.
The traits are the following:
- `From` and `Into` covered in [`from_into`](from_into.rs)
- `TryFrom` and `TryInto` covered in [`try_from_into`](try_from_into.rs)
- `AsRef` and `AsMut` covered in [`as_ref_mut`](as_ref_mut.rs)
Furthermore, the `std::str` module offers a trait called [`FromStr`](https://doc.rust-lang.org/std/str/trait.FromStr.html) which helps with converting strings into target types via the `parse` method on strings. If properly implemented for a given type `Person`, then `let p: Person = "Mark,20".parse().unwrap()` should both compile and run without panicking.
These should be the main ways ***within the standard library*** to convert data into your desired types.
#### Book Sections
These are not directly covered in the book, but the standard library has great documentation for [conversions here](https://doc.rust-lang.org/std/convert/index.html). The `FromStr` trait is also covered [here](https://doc.rust-lang.org/std/str/trait.FromStr.html).

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// AsRef and AsMut allow for cheap reference-to-reference conversions.
// Read more about them at https://doc.rust-lang.org/std/convert/trait.AsRef.html
// and https://doc.rust-lang.org/std/convert/trait.AsMut.html, respectively.
// Obtain the number of bytes (not characters) in the given argument
// Add the AsRef trait appropriately as a trait bound
fn byte_counter<T>(arg: T) -> usize {
arg.as_ref().as_bytes().len()
}
// Obtain the number of characters (not bytes) in the given argument
// Add the AsRef trait appropriately as a trait bound
fn char_counter<T>(arg: T) -> usize {
arg.as_ref().chars().collect::<Vec<_>>().len()
}
fn main() {
let s = "Café au lait";
println!("{}", char_counter(s));
println!("{}", byte_counter(s));
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn different_counts() {
let s = "Café au lait";
assert_ne!(char_counter(s), byte_counter(s));
}
fn same_counts() {
let s = "Cafe au lait";
assert_eq!(char_counter(s), byte_counter(s));
}
}

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// The From trait is used for value-to-value conversions.
// If From is implemented correctly for a type, the Into trait should work conversely.
// You can read more about it at https://doc.rust-lang.org/std/convert/trait.From.html
#[derive(Debug)]
struct Person {
name: String,
age: usize,
}
// We implement the Default trait to use it as a fallback
// when the provided string is not convertible into a Person object
impl Default for Person {
fn default() -> Person {
Person {
name: String::from("John"),
age: 30,
}
}
}
// Your task is to complete this implementation
// in order for the line `let p = Person::from("Mark,20")` to compile
// Please note that you'll need to parse the age component into a `usize`
// with something like `"4".parse::<usize>()`. The outcome of this needs to
// be handled appropriately.
//
// Steps:
// 1. If the length of the provided string is 0, then return the default of Person
// 2. Split the given string on the commas present in it
// 3. Extract the first element from the split operation and use it as the name
// 4. Extract the other element from the split operation and parse it into a `usize` as the age
// If while parsing the age, something goes wrong, then return the default of Person
// Otherwise, then return an instantiated Person onject with the results
impl From<&str> for Person {
fn from(s: &str) -> Person {
}
}
fn main() {
// Use the `from` function
let p1 = Person::from("Mark,20");
// Since From is implemented for Person, we should be able to use Into
let p2: Person = "Gerald,70".into();
println!("{:?}", p1);
println!("{:?}", p2);
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_default() {
// Test that the default person is 30 year old John
let dp = Person::default();
assert_eq!(dp.name, "John");
assert_eq!(dp.age, 30);
}
#[test]
fn test_bad_convert() {
// Test that John is returned when bad string is provided
let p = Person::from("");
assert_eq!(p.name, "John");
assert_eq!(p.age, 30);
}
#[test]
fn test_good_convert() {
// Test that "Mark,20" works
let p = Person::from("Mark,20");
assert_eq!(p.name, "Mark");
assert_eq!(p.age, 20);
}
}

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// This does practically the same thing that TryFrom<&str> does.
// Additionally, upon implementing FromStr, you can use the `parse` method
// on strings to generate an object of the implementor type.
// You can read more about it at https://doc.rust-lang.org/std/str/trait.FromStr.html
use std::str::FromStr;
#[derive(Debug)]
struct Person {
name: String,
age: usize,
}
// Steps:
// 1. If the length of the provided string is 0, then return an error
// 2. Split the given string on the commas present in it
// 3. Extract the first element from the split operation and use it as the name
// 4. Extract the other element from the split operation and parse it into a `usize` as the age
// If while parsing the age, something goes wrong, then return an error
// Otherwise, then return a Result of a Person object
impl FromStr for Person {
type Err = String;
fn from_str(s: &str) -> Result<Person, Self::Err> {
}
}
fn main() {
let p = "Mark,20".parse::<Person>().unwrap();
println!("{:?}", p);
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn empty_input() {
assert!("".parse::<Person>().is_err());
}
#[test]
fn good_input() {
assert!("John,32".parse::<Person>().is_ok());
}
#[test]
#[should_panic]
fn missing_age() {
"John".parse::<Person>().unwrap();
}
}

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// TryFrom is a simple and safe type conversion that may fail in a controlled way under some circumstances.
// Basically, this is the same as From. The main difference is that this should return a Result type
// instead of the target type itself.
// You can read more about it at https://doc.rust-lang.org/std/convert/trait.TryFrom.html
use std::convert::{TryInto, TryFrom};
#[derive(Debug)]
struct Person {
name: String,
age: usize,
}
// Your task is to complete this implementation
// in order for the line `let p = Person::try_from("Mark,20")` to compile
// and return an Ok result of inner type Person.
// Please note that you'll need to parse the age component into a `usize`
// with something like `"4".parse::<usize>()`. The outcome of this needs to
// be handled appropriately.
//
// Steps:
// 1. If the length of the provided string is 0, then return an error
// 2. Split the given string on the commas present in it
// 3. Extract the first element from the split operation and use it as the name
// 4. Extract the other element from the split operation and parse it into a `usize` as the age
// If while parsing the age, something goes wrong, then return an error
// Otherwise, then return a Result of a Person object
impl TryFrom<&str> for Person {
type Error = String;
fn try_from(s: &str) -> Result<Self, Self::Error> {
}
}
fn main() {
// Use the `from` function
let p1 = Person::try_from("Mark,20");
// Since From is implemented for Person, we should be able to use Into
let p2: Result<Person, _> = "Gerald,70".try_into();
println!("{:?}", p1);
println!("{:?}", p2);
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_bad_convert() {
// Test that John is returned when bad string is provided
let p = Person::try_from("");
assert!(p.is_err());
}
#[test]
fn test_good_convert() {
// Test that "Mark,20" works
let p = Person::try_from("Mark,20");
assert!(p.is_ok());
let p = p.unwrap();
assert_eq!(p.name, "Mark");
assert_eq!(p.age, 20);
}
#[test]
#[should_panic]
fn test_panic_empty_input() {
let p: Person = "".try_into().unwrap();
}
#[test]
#[should_panic]
fn test_panic_bad_age() {
let p = Person::try_from("Mark,twenty").unwrap();
}
}

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// Type casting in Rust is done via the usage of the `as` operator.
// Please note that the `as` operator is not only used when type casting.
// It also helps with renaming imports.
// The goal is to make sure that the division does not fail to compile
fn average(values: &[f64]) -> f64 {
let total = values
.iter()
.fold(0.0, |a, b| a + b);
total / values.len()
}
fn main() {
let values = [3.5, 0.3, 13.0, 11.7];
println!("{}", average(&values));
}

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If you've learned from the sample solutions, I encourage you to come
back to this exercise and try it again in a few days to reinforce
what you've learned :)"""
# TYPE CONVERSIONS
[[exercises]]
name = "using_as"
path = "exercises/conversions/using_as.rs"
mode = "compile"
hint = """
Use the `as` operator to cast one of the operands in the last line of the
`average` function into the expected return type."""
[[exercises]]
name = "from_into"
path = "exercises/conversions/from_into.rs"
mode = "test"
hint = """
Follow the steps provided right before the `From` implementation"""
[[exercises]]
name = "try_from_into"
path = "exercises/conversions/try_from_into.rs"
mode = "test"
hint = """
Follow the steps provided right before the `From` implementation.
You can also use the example at https://doc.rust-lang.org/std/convert/trait.TryFrom.html"""
[[exercises]]
name = "as_ref_mut"
path = "exercises/conversions/as_ref_mut.rs"
mode = "test"
hint = """
Add AsRef<str> as a trait bound to the functions."""
[[exercises]]
name = "from_str"
path = "exercises/conversions/from_str.rs"
mode = "test"
hint = """
If you've already solved try_from_into.rs, then this is almost a copy-paste.
Otherwise, go ahead and solve try_from_into.rs first."""